1. Field of the Invention
The present invention relates generally to methods and systems for scrambling transmitted information, and more specifically, to a simplified scrambling scheme that unifies all signals with a common reference phase.
2. Description of the Related Art
Digital Direct Broadcast Systems (DBS), such as DIRECTV®, which is provided by the assignee of the present invention, have become very successful. However, as such systems evolve, there is an increasing demand for additional bandwidth to carry an ever-increasing set of audio, video and data services.
In satellite television, there is a constant need for additional throughput to adequately accommodate the ever-increasing demands with respect to the video and data services which they provide. With respect to developing their next generation systems, more efficient forward error correction (FEC) codes such as low-density parity check (LDPC) codes, turbo codes, etc., are under investigation in order to achieve the aforementioned goal. To use these highly efficient FEC codes, a frame header is pre-inserted to modulated data to ensure that the boundaries of code frames can be easily identified by the decoder. Also, since these codes are often operated over channels with very low carrier-to-noise ratio (CNR) and in the presence of low noise block (LNB) and other phase noise, pilot symbols are inserted periodically to improve the performance of carrier synchronization.
Header and pilot symbols are essential in the next generation of satellite television broadcasting systems to ensure the quality of timing acquisition and frame synchronization as well as carrier (including frequency and phase) acquisition and tracking. There is a need to improve demodulation performance of systems with header/pilot symbols. The present invention satisfies this need.